Process for the production of absorbing material with an improved degradability and absorption for water, aqueous solutions and body liquids, and its use in hygienic articles and for soil conditioning

ABSTRACT

A process for the production of absorbing agents for water, aqueous solutions and body liquids consisting of at least two components A and B, whereby component A comprises a water-swellable, synthetic polymer or copolymer and component B comprises a natural or synthetic polymeric compound which at normal temperature is a pourable powder and is partially soluble or insoluble in water. Component B is added to component A in dry or partially swollen form during component A&#39;s production process after a monomer conversion of at least 30%, preferably at least 60% is attained, and is then mixed with the polymer gel of component A and subsequently dried. The invention further relates to the use of the absorbing agent for the absorption and/or retention of water and/or aqueous solutions, in particular of aqueous body liquids, such as urine or blood, in absorbent expendable products for hygienic, surgical and other medical purposes, such as diapers, tampons, and sanitary napkins; for the absorption and/or retention of water and/or aqueous solutions and subsequent controlled release of water and/or the substances dissolved in the aqueous medium to other bodies, as well as for drying gases and/or liquids, preferably organic liquids and solvents which are not miscible in water.

This application is a continuation of application Ser. No. 08/057,194,filed May 3, 1993, now abandoned, which is a continuation of Ser. No.07/761,072, filed Sep. 17, 1991, now abandoned.

The present invention relates to a process for the production ofabsorbers consisting of a combination of synthetic polymers and,preferably, natural polymers, such as polysaccharides, which absorbersrapidly absorb water and aqueous liquids, and are used, e.g., forabsorptive expendable products in hygienic articles, such as diapers andsanitary towels, and for other medical purposes, or as water-storingsoil conditioners.

Absorbents having a high absorption capacity for water and body liquidsare known. Those belonging to the fully synthetic absorbing agents arecross-linked polymers and copolymers on the basis of acrylic ormethacrylic acid (German OS Offenlegungsschrift, publication of a Germanpatent application! Nos. 24 29 236, 26 14 662, 27 12 043, 26 53 135, 2650 377, 28 13 634; U.S. Pat. Nos. 4,018,951, 3,926,891, 4,066,583,4,062,817), maleic acid derivatives (according to U.S. Pat. No.4,041,228), or acrylamidopropane sulfonic acid copolymers (according toGerman Pat. No. 31 24 008). These known synthetic absorbers arepractically water-insoluble, absorb the multiple amount of their weightof water, urine, or other aqueous solutions, however, are relativelyresistant to biodegradability.

Other products were produced on a starch basis, e.g., starchacrylonitrile graft polymers (U.S. Pat. Nos. 3,997,484, 3,661,815,4,155,888, 3,935,099), gelatinized starch derivatives (German OS 27 02781), or on a cellulose basis, such as derivatives of alkyl- orhydroxyalkyl cellulose (JP-Pat. No. 77/125 481), carboxymethylcellulose(BE-Pat. No. 862 130 and GB-Pat. No. 1 59 949) and on a polysaccharidebasis (German OS 26 50 377). Although these products, such as the starchpolymers grafted with acrylonitrile or acrylic acid, belong to thedecomposable products, their production is very expensive, and theamount of the natural product in the end product is very limited due tothe high viscosity of the reaction medium, e.g., in case of a monomersolution with dissolved starch. The monomer solution according toEuropean Pat. No. 0 372 981, Example 11, for instance, only containsapproximately 4%-wt. of dissolved starch, relative to the total batch.

According to German Pat. No. 21 43 549, starch products, dextrin, orflour are used to powder the gelatinous granular material ofpolyacrylamide polymers to obtain storable, non-agglomerating,dimensionally stable gelatinous granular material with a high content ofwater. Said material is proposed for the use as water-solubleflocculation and sedimentation auxiliary agents.

In this case, the starch is distributed only on the surface of thehydrous polymer gel particles of the water-soluble product. On the firstcontact with water, the starch is substantially washed off the surfaceof the powdered polymer gel. There is no incorporation of the starchinto the swollen polyacrylamide gel.

As a consequence, a procedure of directly adding the natural product(referred to as "component B" hereinafter) to the monomer solution ofcomponent A (synthetic polymer), homogenizing, and then starting thepolymerization may be carried out only in case of low contents of 2 to amaximum of 5%-wt. of component B in the monomer solution. For technicaland economic reasons, however, the monomer concentration of the monomersolution is between 20 to 30%-wt. Such processes are described, e.g., byGerman Pat. No. 26 12 846, British Pat. No. 1490128, and European Pat.No, 0 189 163, Efforts to dissolve quantities above 5%-wt. of componentB in the monomer solution, result in highly viscous to gel-like monomersolutions which cannot be stirred and thus prevent homogeneous mixingwith the catalyst solutions so that an even polymerization conducted toa high reaction degree is rendered impossible.

According to German OS 22 64 027, inert filling agents, such as woodflour, pulp fibers, cellulose or nylon floccules, slag, clay, fly ash,coal dust, and fertilizers, are used as additives during thecrosslinkage of the water-soluble polymers. The uricrosslinked,water-soluble polymers or copolymers, respectively, are mixed as drypowder with the inert fillers; after the mixture has been sprayed with15 to 85%-wt., or even more, water (in the major part of the examples200 to 400%-wt. water, relative to the mixture of polymer and filler areused) the resultant water-containing granulate is cross-linked byionizing radiation (0.05 to 20.0 MeV). After drying, a partiallywater-insoluble polymeric absorber results which absorbancy for water isapproximately five- to forty-fold the amount of the dry weight.

It is the object of the present invention to provide a process enablingthe incorporation of the known synthetic polymers with high absorptioncapacity for water and aqueous liquids, such as urine or blood, and usedas absorbents by means of additives which on their own have acomparatively low absorption capacity for such liquids, withoutsignificantly deteriorating the absorption capacity of the end product,even if larger amounts of poorly absorbing additives are incorporated.Also the degradability is improved in certain cases.

This object is achieved according to the present invention by thecharacterizing features of claim 1.

The manufacture of component A is carried out according to knownmethods. It may be effected discontinuously as swollen polymer gel in apolymerization vessel, or continuously on a continuous belt, Accordingto German Pat. No. 35 44 770, e.g., the polymerization is carried out inan aqueous solution containing the water-soluble monomer and,optionally, the comonomers at a concentration of 2.2 to 8.3 mols ofpolymerizable double bonds per kilogram of monomer solution, inparticular 3.5 to 6.25 mols (corresponding to 16 to 60%-wt.,particularly 25 to 45%-wt. acrylic acid, if it is used as monomer) andwithin a temperature range of approximately -10° to 120° C.

The polymers of acrylic acid and methacrylic acid alone as homopolymeror as copolymer are primarily suitable for the use as component A, butalso the polymers of other water-soluble monomers, such as acrylamide,as well as polymerizable acids and the salts thereof, in particularmaleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, or2-acrylamido-2-methylpropane sulfonic acid. Further examples arehydroxyl-groups-containing esters of polymerizable acids, in particularthe hydroxyethyl- and hydroxy-propyl esters of acrylic and methacrylicacid; as well as amino-groups-containing and ammonium-groups-containingesters and amides of polymerizable acids, such as the dialkylaminoesters, in particular the dimethyl- and the diethylaminoalkyl esters ofacrylic and methacrylic acid, as well as the trimethyl- andtriethylammonium alkylesters and the corresponding amides. In addition,small amounts of cross-linking monomers, e.g., monomers having more thanone polymerizable group within the molecule, are polymerized togetherwith the above-mentioned monomers.

The above-mentioned monomers may be polymerized alone to formcross-linked homopolymers, or with one another to form cross-linkedcopolymers.

In addition, small amounts of monomers which are slightly or eveninsoluble in water, such as (meth)acrylonitrile, vinyl pyridine, andvinyl acetate may be copolymerized, such as the esters of acrylic and/ormethacrylic acid with C₁ -C₁₀ -alcohols, styrene and alkylated styrenes.In general, the proportion of water-soluble monomers is in the range of40 to 100%-wt., relative to the total amount of monomers. The proportionof the cross-linking monomers is in the range of 0 to 20%-wt.,preferably 0.01 to 2.0%-wt., relative to the total monomer amount. Ingeneral, the amount of water-insoluble, hydrophobic monomers is 0 to40%-wt. of the monomers.

Examples of cross-linking monomers include bi- and polyfunctionalmonomers, e.g., amides, such as the methylene bisacryl- or-methacrylamide or ethylene bisacrylamide, in addition esters of theunsaturated mono- or polycarboxylic acids of polyols, such asdiacrylates or triacrylates, e.g., butanediol- or ethylene glycoldiacrylate or -methacrylate, trimethylolpropane triacrylate, as well asvinyl methacrylate and allyl compounds, such as allyl(meth)acrylate,triallyl cyanurate, maleic acid diallyl ester, polyallyl ester,tetraallyl oxiethane, triallylamine, tetraallyl ethylene diamine, allylester of the phosphoric acid or phosphorous acid, respectively, as wellas cross-linkable monomers, such as the N-methylol compounds of amides,such as methacrylamide or acrylamide and the ethers derived therefrom.

The polymerization may be initiated by chemical catalysis and/orhigh-energy radiation/light. Suitable catalysts, for example, are peroxycompounds, such as potassium peroxydisulfate, hydrogen peroxide, organicperoxides, such as benzoyl peroxide, tert-butyl hydroperoxide,tert-butyl perpivalate; redox systems, such aspotassium-peroxydisulfate-sodium-disulfite, hydrogen peroxidehydroxylamine chloride, or azoinitiators, such as AIBN2,2'-azobis-(isobutyronitrile)! or2,2'-azobis(2-amidinopropane)dihydrochloride. Examples of suitablephotoinitiators include benzoin and the derivatives thereof, e.g.,benzoin ether, such as benzoin-ethyl-propyl-ether, benzil and thederivatives thereof, such as benzil ketals or aryl diazonium salts,acetophenone derivatives, and others, alone or in admixtures. Ingeneral, the content of photoinitiators is in the range of 0.002 to2.0%-wt., preferably 0.01 to 0.2%-wt., relative to the monomers used.The content of catalysts generally is in the range of 0.02 to 5.0%-wt.,preferably between 0.20 to 2.0%-wt., relative to the monomers.

According to the present invention, natural polymers based onpolysaccharide are used as component B, examples thereof includemodified cellulose and cellulose derivatives, e.g., alkyl-,hydroxyalkyl-, carboxymethylcellulose, gum resins, e.g., guar gum,locust bean gum, tragacanth gum, gum arabic, pectin, etc.; starch andstarch derivatives, such as corn starch, grain starch, potato starch,amylose, amylopectin, dextrin, dextran, modified starch, hydroxyethylstarch, cationic starch, starch graft polymers, etc.

In addition to said natural polymers used as component B, also othermaterials with a large surface may be used, e.g., fibrous material ofnatural fibers, preferably fibers of cotton, hemp, wool, and silk,furthermore fibrous material of cellulose fibers, such as viscose,acetate- and triacetate fibers, or of synthetic fibers based onpolyester, polyolefins, polyacrylonitrile, polyamide, polyvinyl alcohol,polyvinyl acetate, and polyvinyl chloride, polyurethane, polyvinyl urea,as well as the copolymers of these polymers. The fibrous materials maypreferably be incorporated into component A in the form of short fibershaving a length of 0.1 to 60 mm.

Additional materials may also be used as additive, for example,odoriferous substances to perfume the final product, disinfectants,antibacterial agents, but also neutral fillers, such as wood flour,peat, ground shells of walnuts or pomaceous fruit, chitin-containingflour, sand, garden mold, or other extenders.

Finally, it is also possible to add as component B only the finelyground component A in dried powder or partially swollen form to thepolymer gel of component A.

The process according to the present invention consists in the fact thatcomponent B is added to the swollen polymer gel of component A as apowder in dry or slightly moist or swollen form during the manufactureof the synthetic-polymer (component A). Advantageously, component B isadded to the swollen polymer gel of component A only during the endphase of the production of component A, i.e., not before a reactionconversion of more than 30%, preferably more than 60%, and in particularpreferred more than 95% is achieved, and it is then mixed with thepolymer gel and subsequently dried.

Mixing the two components may be carried out in a suitable mixer.Advantageously, a mixer with rotary stirring mechanism is used. Asuitable mixer, for example, consists of a vertically or horizontallypositioned metal cylinder the stirrer of which is provided with guideblades thoroughly wiping the walls of the mixer drum.

A trough kneader with double-U-shaped cross-section may also be used tomix the two components A and B evenly. Within said trough, a pair ofkneading shafts is moving in the same or opposite direction at the sameor different speed; the form of the blades may also be selected inaccordance with the material to be mixed. For continuous operation, thetrough kneader may be provided with a discharging cylinder and adischarge screw which either works in reverse rotation to the interiorof the trough thus intensifying the mixing and kneading process, or isswitched in reversed direction of the material discharge.

Examples of other suitable devices for continuous operation include:single-shaft mixers, such as a single-screw extruder, ko-kneaders,two-shaft mixers with twin worm operating in the same or oppositedirection, conical cotruder-screw, double-shaft continuous kneader, andcontinuous multi-shaft devices, e.g., a four-screw extruder.

After mixing, the mass of polymer gel is dried at a temperature within arange of 50° to 160° C. An end product is obtained in which thecomponent B (e.g., a natural polymer) is incorporated in the syntheticpolymer in such a way that the water-extractable portions of the endproduct--compared to a physical mixture of components A and B--aresignificantly smaller, preferably 30%-wt. and in particular below20%-wt.

The incorporation of component B into the synthetic polymer may beintensified by adding different, above-mentioned catalysts in an amountof 0.01 to 2.0%-wt., and/or the above-mentioned polyfunctional monomersin an amount of 0.05 to 5.0%-wt. to component B or component A. Thecatalysts or polyfunctional compounds may be sprayed, for example as asolution, on component A or B either prior to or during mixing.

Low- or high-molecular, water-soluble or water-swellable polymers on asynthetic or natural basis (e.g., polysaccharides in dissolved orswollen condition) may additionally be used as auxiliary binding agentsto support the linkage of the two components A and B. Examples ofwater-soluble or water-swellable polymers on a synthetic basis arepolymers or copolymers based on (meth-)acrylic acid or (meth-)acrylicacid derivatives, such as the homo- or copolymers of acrylic acid,methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, of thesalts of these acids, of the acrylamide or methacrylamide, with oneanother or with vinyl pyrrolidone and/or vinyl acetate, as well aspolyvinyl alcohol.

However, it is also possible to employ low- or high-molecular polymersbeing present as emulsion polymers in an aqueous dispersion in the formof tiny spherical particles solubilized by an emulsifier, whereby bothforms of emulsion "oil-in-water" (for water-insoluble polymers) and"water-in-oil" (for water-soluble polymers) are possible. As isgenerally known, the oil phase in most cases consists of organicsolvents which are not miscible with water, such as aliphatic oraromatic hydrocarbons (e.g., hexane, white oil).

Examples of polymers capable of forming oil-in-water emulsions includepolymers of butadiene, styrene, isoprene, chloroprene, acrylonitrile,vinyl acetate, vinyl- and vinylidene chloride, alkylacrylates andalkylmethacrylates, and copolymers of these monomers with one another orwith methyl styrene, isobutylene, or ethylene.

Examples of polymers which are used in water-in-oil emulsions includethe above-mentioned water-soluble or water-swellable polymers orcopolymers on the basis of (meth-)acrylic acid derivatives, which may becrosslinked or not.

The following examples demonstrate that the end products of component Aand B produced according to the process of the present invention have animproved absorption capacity for synthetic model urine solution(examples 1 to 8) and they exhibit a considerably improved degradability(example 16).

The final product consists of the components A and B at a weight ratioof 20 to 98%-wt, preferably 40 to 95%-wt. of component A, and 2 to80%-wt., preferably 5 to 60%-wt. of component B.

Test methods

1) In order to determine the rate of absorption, the absorp-tion ofmodel urine is carried out according to the Demand-Absorbency-Test(DAT-method according to W. F. Schlauch, lecture index 1978, Amsterdam);the absorption rate after 60 seconds, as well as the maximum absorptionand the retention are determined. The measuring instrument consists of aburette filled with the model urine solution (2.0% urea, 0.9% NaCl, 0.1%MgSO₄, and 0.06% CaCl₂, dissolved in distilled water) and a tableprovided with an outlet opening for the model urine solution connectedto the measuring burette. On the table, which was covered with a thinnon-woven (10×13.5 cm), 0.5 g of the product according to the presentinvention, mixed with 5 mg Aerosil 200 (Degussa AG), is evenly sprinkledon the middle of the liquid outlet in the form of a circular area havinga diameter of 4.5 cm. The contact of the model urine solution with thepowder product is effected by closing the hose and slight pressureloading; the solution of model urine may now be absorbed by the productaccording to the present invention. After 20 to 30 minutes, the absorbedamount of model urine solution is read as maximum value. Subsequently,the retention was determined by loading the swollen gel with a weight of10 g/cm² ; loading is effected for 5 minutes. The determined retentionvalues are tabulated in the examples.

2) A tea bag test was carried out as additional method to determine therate of liquid absorption. The liquid absorption of 0.2 g test substancewithout added Aerosil was gravimetrically determined in a tea bag after10 minutes (maximum value) and after centrifuging, e.g., in a commercialspin dryer at 1400 rpm, this value was then converted to 1 g of product(retention value). The aqueous 0.9% NaCl-solution was used as testliquid.

3) Artificial decomposition conditions effected by irradiation similarto daylight were simulated with a Xenotest lamp and exposure times of30, 60, and 90 minutes using a polymer gel swollen with water (200 gwater per 1 g product). The swollen polymer gel was exposed to theXenotest lamp, and after certain intervals of time, the degradability ofthe polymer gel was assessed according to a scale with 1 to 8 grades(Example 16).

Grade 1: gel structure unchanged

Grade 2: gel structure slightly changed

Grade 3: gel structure still detectable, but slight flow

Grade 4: gel structure extremely flown

Grade 5: gel structure not detectable, a highly viscous liquid

Grade 6: low viscous liquid

Grade 7: liquid ressembling water

Grade 8: water completely evaporated

The Xenotest lamp corresponds to natural daylight in the spectralregion; the method was developed by Cassella Farbwerke, Mainkur AG,Frankfurt, FRG.

EXAMPLES 1 TO 3

330 g acrylic acid, 2.6 g N,N'-methylene bisacrylamide (0.8%-wt.,relative to acrylic acid) were dissolved in 1000 ml water in apolymerization vessel and partially neutralized with 130 g sodiumhydrogencarbonate. The catalyst components (0.3 g azobisamidine propanedihydrochloride, 0.6 g potassium peroxide disulfate, and 1.2 g sodiumdisulfite) dissolved in I20 ml water, were added at room temperatureinitiating the adiabatic polymerization. The resulting polymer gel wasreduced in size, evenly sprayed with an aqueous solution of 2000 ppm(relative to the dry substance of the polymer gel) sodiumperoxidisulfate, and mixed with component B.

Mixing of the polymer gel A with component B was carried out in a mixerproduced with rotating stirring device. The device consists of avertically or horizontally positioned metal cylinder (volume approx.6000 ml), the mixing device of which is provided with guide blades tostrip off thoroughly the walls of the mixing cylinder. After reaching arotation speed of 300 rpm, a fluidized bed on the total length of themetal cylinder forms through the expelled individual particles of themass when the rotary guide blades of the mixing device emerge. At thisstage, the two components are evenly mixed and kneaded.

Subsequently, the resulting mass of polymer gel was dried within arecirculating air dryer at 120° C. and then ground. Starch being solublein cold water was used as component B at different ratios. Theabsorption capacity of the end products was determined according to theDAT-method (Table 1).

                  TABLE 1                                                         ______________________________________                                                      Component B                                                     Component A   starch sol-        DAT-values                                   acrylic acid  uble in cold       retention                                    polymer       water              (a)   (b)                                    %-wt.         %-wt.              (ml/g)                                                                              (ml/g)                                 ______________________________________                                              100         0                26.9  26.9                                       0           100        smaller                                                                             1.0   --                                   Ex. 1:                                                                              91          9                26.0  28.6                                 Ex. 2:                                                                              83          17               23.7  28.5                                 Ex. 3:                                                                              67          33               20.0  29.8                                 ______________________________________                                         Note:                                                                         The DATvalue retention (a) relates to 1 g of the product composed of          components A and B, retention (b) relates to 1 g of component            

EXAMPLES 4 AND 5

Component A was produced according to the method as in Examples 1 to 3and processed with alginate used as component B, The results aresummarized in Table 2.

                  TABLE 2                                                         ______________________________________                                        Component A                DAT-values                                         acrylic acid   Component B retention                                          polymer        alginate    (a)      (b)                                       %-wt.          %-wt.       (ml/g)   (ml/g)                                    ______________________________________                                               100         0           26.9   26.9                                           0           100         12.1   --                                      Ex. 4: 83          17          27.0   32.6                                    Ex. 5: 67          33          26.5   39.6                                    ______________________________________                                         Note:                                                                         The DATvalue retention (a) relates to 1 g of the product composed of          components A and B, retention (b) relates to 1 g of component A in the        product.                                                                 

EXAMPLES 6 TO 8

A polymer gel having a cross-linking agent content of 0.6%-wt. (relativeto polyacrylic acid) was produced according to the procedure of Examples1 to 3; employed as component A, it was mixed with different amounts ofcorn starch in the described mixer and then processed according to thesame manner as in Examples 1 to 3. In addition to the absorptioncapacity, the content of components A and B in the portions which areextractable with water was determined. The results are listed in thefollowing table.

                  TABLE 3                                                         ______________________________________                                        Component A                     tea-bag-test-values                           acrylic acid Component B        retention                                           polymer    corn starch      (a)    (b)                                        %-wt.      %-wt.            (ml/g) (ml/g)                               ______________________________________                                              100        0                26.9   26.9                                       0          100        smaller                                                                             1.0    --                                   Ex. 6:                                                                              91         9                26.0   28.2                                 Ex. 7:                                                                              83         17               25.1   30.2                                 Ex. 8:                                                                              71         29               24.8   34.9                                 ______________________________________                                                Soluble portions                                                                Component A          Component B                                              %                    %                                              ______________________________________                                                  3.5                  --                                                       --                   --                                             Example 6:                                                                              3.3          smaller  1.0                                           Example 7:                                                                              3.9                  --                                             Example 8:                                                                              4.5                  11.0                                           ______________________________________                                         Note:                                                                         The tea bag testvalue retention (a) relates to 1 g of the product compose     of components A and B, retention (b) relates to 1 g of component A within     the product.                                                             

EXAMPLES 9 AND 10

In a polymerization vessel, 370 g acrylic acid and 3.1 g N,N'-methylenebisacrylamide were dissolved in 410 ml water and neutralized with 460 gcaustic-soda solution (45%). The catalyst components (0.26 azobisamidinepropane dihydrochloride, 0.06 g benzil dimethyl ketal (Irgacure 651),and 0.26 g t-butyl hydroperoxide, dissolved in water) were added at roomtemperature and the adiabatic polymerization was started by UV-light.The achieved degree of reaction was 99.5%. The resulting polymer gel wasreduced in size, dried to a water content of 8%-wt., ground and mixedwith corn starch and moist viscose short fibers in a mixer according toExamples 1 to 3, and again dried a% 120° C. The results are listed in%he following table.

                                      TABLE 4                                     __________________________________________________________________________    Component A Component B                                                                            tea bag test-values                                      acrylic acid                                                                              corn                                                                              viscose        retention                                      polymer     starch                                                                            fibers                                                                             maximum   (a) (b)                                        (%-wt.)     (%-wt.)                                                                           (%-wt.)                                                                            (ml/g)    (ml/g)                                                                            (ml/g)                                     __________________________________________________________________________        100     0   0    39.8      24.2                                                                              24.2                                           0       100 0    4.0  smaller                                                                            1.0 --                                             0       0   100  5.8       1.0 --                                         Ex. 9:                                                                            80      5   15   37.1      23.8                                                                              29.7                                       Ex. 10:                                                                           50      5   45   31.5      15.4                                                                              30.8                                       __________________________________________________________________________     Note:                                                                         The tea bag test values maximum and retention (a) relate to 1 g of the        product composed of components A and B, retention (b) relates to 1 g of       component A in the product                                               

EXAMPLES 11 AND 12

According to the method of Examples 1 to 3, a polymer gel with a contentof cross-linking agent of 0.4%-wt. (relative to polyacrylic acid) wasproduced and--used as component A--mixed and processed in a troughkneader with corn starch and different amounts of polyamide short fibers(1.0 mm, 6.7 dtex). The trough kneader (Werner & Pfleiderer, Stuttgart)consisted of a housing with a double-U-shaped cross-section, in which apair of kneading shafts with two toothed, oppositely runningsigma-blades moved. Processing within the kneader was terminated after 5minutes; the resultant kneading mass was reduced in a meat grinder anddried at 120° C. The composition and the tea bag test-values are listedin the following table.

                                      TABLE 5                                     __________________________________________________________________________    Component A Component B                                                                            tea bag test-values                                      acrylic acid                                                                              corn                                                                              polyamide      retention                                      polymer     starch                                                                            fibers                                                                             maximum   (a) (b)                                        (%-wt.)     (%-wt.)                                                                           (%-wt.)                                                                            (ml/g)    (ml/g)                                                                            (ml/g)                                     __________________________________________________________________________        100     0   0    39.8      30.2                                                                              30.2                                           0       100 0    4.0  smaller                                                                            1.0 --                                             0       0   100  4.5  smaller                                                                            1.0 --                                         Ex. 11:                                                                           90      5   5    39.4      27.5                                                                              30.6                                       Ex. 12:                                                                           85      5   10   39.8      27.4                                                                              32.2                                       __________________________________________________________________________     Note:                                                                         The tea bag test values maximum and retention (a) relate to 1 g of the        product composed of components A and B, retention (b) relates to 1 g of       component A within the product.                                          

EXAMPLES 13 AND 14

A polyacrylic acid polymer having a content of cross-linking agent of0.8%-wt. was produced according to the process as in Example 9; it wasthen dried and ground. The finely ground size fraction of smaller than150 μm was mixed with cellulose fibers (Arbocell 800, Rettenmayer,Holzkirchen) and processed in dry condition, or partially made into apaste with water, in a trough kneeder as in Example 11 with the freshlymade polymer gel manufactured according to Example 9. Processing in thekneader was terminated after 5 minutes; the resultant kneading mass wasreduced in a meat grinder and dried at 150° C. The particle-sizedistribution of the end product with a fine-material-portion which wassmaller than 150 μm of 22.6%-wt. may be compared to the particle-sizedistribution of a ground mass from a freshly produced polymer 9granulateof component A without any additives (20.1%-wt. fines smaller than 150μm).

                  TABLE 6                                                         ______________________________________                                                     Component B                                                                   acrylic                                                          Component A  acid polymer                                                     acrylic acid (size fraction                                                                           tea bag test-values                                   polymer      smaller than                                                                             cellulose                                                                              retention                                    (polymer gel)                                                                              150 μm) fibers   (a)   (b)                                    %-wt.        %-wt.      %-wt.    (ml/g)                                                                              (ml/g)                                 ______________________________________                                              100        0          0      26.9  26.9                                       0          0          100    1.6   --                                   Ex. 13:                                                                             82         9          9      22.8  25.1                                 Ex. 14:                                                                             73         18         9      22.3  24.5                                 ______________________________________                                         Note:                                                                         The tea bag test value retention (a) relates to 1 g of the product            composed of components A and B, retention (b) relates to 1 g of component     A in the product.                                                        

EXAMPLE 15

According to the procedure of Example 7, a polymer gel of polyacrylicacid with a cross-linking agent content of 0.3%-wt. was produced, driedand ground. The size fraction of smaller than 150 μm was made into apaste with water and processed as component B fin a trough kneader(Example 14). The resultant kneading mass was reduced in a meat grinderand mixed with freshly produced polymer gel at a Weight ratio of 1:4,dried at 150° C. and ground. The particle-size distribution of the endproduct with a moiety of fines being smaller than 150 μm of 19.5%-wt.may be compared to the particle-size distribution and the fine-grainproportion of a ground material from a freshly produced polymer granularmaterial (20.1%-wt. fines). The end product has a retention of 31.0ml/g.

According to the procedure as in Examples 1 to 3 a polymer gel having acontent of cross-linking agent of 0.6%-wt. (relative to polyacrylicacid) was produced. Used as component A, it was mixed with differentamounts of corn starch in a mixer as in Examples 1 to 3, and processedin the same manner as described in Examples 1 to 4. The powdery endproduct was swollen with water (200 g water per 1 g product), and theswollen gel was irradiated with the xenon test lamp to simulateartificial degradation conditions. After 30, 60, and 90 minutes, thedegradability of the polymer gel was assessed according to a scale withgrades 1 to 8, The results are summarized in the following table.

                  TABLE 9                                                         ______________________________________                                        Component A                                                                   Acrylic acid                                                                              Component B                                                                              Exposure time                                          polymer     Corn starch                                                                              Minutes                                                %-wt.       %-wt.      30        60  90                                       ______________________________________                                        100         0          1         1   2                                        90          10         2         4   5                                        80          20         3         4   6                                        60          40         3         6   7                                        ______________________________________                                    

Grade 1: gel structure unchanged

Grade 2: gel structure slightly changed

Grade 3: gel structure still detectable, but slight flow

Grade 4: gel structure extremely flown

Grade 5: gel structure not detectable, a highly viscous liquid

Grade 6: low viscous liquid

Grade 7: liquid ressembling water

Grade 8: water completely evaporated

EXAMPLE 17

The polymerization was carried out in the trough kneader described inExample 14. During the polymerization the starch was incorporated in thepolymer gel. In the kneader which was blown with nitrogen, 840 g acrylicacid, 5.88 g methylene bisacrylamide were dissolved in 1270 ml waterfirst, and then partially neutralized with 725 g caustic-soda solution(45%). The catalyst components (3.3 g azobisamidine propanedihydrochloride, 3.0 g sodium peroxidisulfate, and 0.05 g ascorbicacid), dissolved in 150 ml water, were added at room temperature; themonomer solution was blown with nitrogen and the adiabaticpolymerization started.

When a polymer conversion of approximately 60% was achieved, 84 g starchsoluble in cold water (10%-wt., relative to acrylic acid) was stirred inportions into the forming soft polymer gel by means of the pair ofkneading shafts and the polymerization was continued. Subsequently, theresultant mass of polymer gel was reduced in size, dried in arecirculating air dryer at 120° C. and then ground.

The absorption capacity of the end product (DAT-values) were 32ml/g--maximum value and 21 ml/g--retention (a).

EXAMPLE 18

The polymerization was started in the trough kneader according to theprocedure as described in Example 17, after a polymer conversion ofapproximately 30% was achieved, 168 g starch being soluble in cold water(20%-wt., relative to acrylic acid) was added to the soft polymer gelwhich was forming. The starch was incorporated in the polymer gel withthe pair of kneading shafts. After the end of polymerization, the massof polymer gel was reduced in size and dried as in Example 17.

The absorption capacity of the final product were 28 ml/g (DAT-maximum)and 20 ml/g--retention (a).

It is understood that the specification and examples are illustrativebut not limitative of the present invention and that other embodimentswithin the spirit and scope of the invention will suggest themselves tothose skilled in the art.

I claim:
 1. A process for the production of a water absorptive materialcomprising1. polymerizing a monomer mixture comprising by weighta).40-100% monomeric units selected from the group consisting ofpolymerizable acids, and salts, esters and amides of such acids, b).0.01-2.0% of a cross-linking monomer having at least two functionalgroups, and c). 0-40% of a water-insoluble monomer,said monomers, uponpolymerization, forming a water-swellable, synthetic polymer orcopolymer, to a momomer conversion of at least 30% to form a polymer gel(component A),
 2. blending with said polymer gel a polysaccharide whichis a pourable powder at normal temperature and is only partially solubleor insoluble in water (component B), said polysaccharide being blendedwith said polymer gel in dry or partially swollen form during thepolymerization process of component A after said monomer conversion ofat least 30%.
 3. drying the blend of the polymer gel and thepolysaccharide to form a water-swellable polymer or copolymer basedcomposition which retains high water absorptive capacity even though thepolysaccharide with a low water absorptive capacity is blendedtherewith, the amount of water extractables from the product ofcomponent A and component B being less than the water extractables fromthe physical blend of component A and component B.
 2. The processaccording to claim 1, wherein component B is added to component A onlyduring the end phase of the production process of component A after amonomer conversion of more than 80% is attained.
 3. The processaccording to claim 1, wherein component B is used in dried form as apowder.
 4. The process according to claim 1, wherein component B is usedin slightly swollen form.
 5. The process according to claim 1, wherein abond between component A and B is achieved by adding at least oneradical-forming catalyst to component A or B.
 6. The process accordingto claim 1, wherein, in addition to component B, a natural or asynthetic fiber is added.
 7. The process according to claim 6, whereinsaid natural fiber is a fiber selected from the group consisting ofwool, silk, cotton or cellulose and said synthetic fiber is a fiberselected from the group consisting of polyester, polyolefin, polyamide,polyvinyl alcohol, polyurethane, polyurea, or polyacrylonitrile.
 8. Theprocess according to claim 1, wherein a neutral filler alone or inadmixture with component B, or the ground component A itself, in theform of a powder or partially swollen, is incorporated into component A.9. The process according to claim 1, wherein at least one of peat, sand,clay, garden mold, ground shells of nuts or pomaceous fruit, Wood flourand chitin-containing flour is used as neutral filling agent.
 10. Theprocess according to claim 1, wherein the absorbing material consistsessentially of A and B, component B consists essentially of apolysaccharide and component A is a copolymer consisting essentiallyofa) 40-100%-wt. of a water-soluble monomer selected from the groupconsisting of polymerizable acids, the salts thereof, thehydroxy-group-, amino-group-or ammonium-group-containing esters oramides of such acids, and acrylamide. b) 0.01-2.0%-wt. of a crosslinkingmonomer having at least two functional groups, and c) 0-40%-wt. of awater-insoluble monomer.
 11. The process according to claim 1, whereincomponent A is a cross-linked polymer or copolymer comprising monomericunits of a polymerizable acid selected from the group consisting ofacrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconicacid, vinyl sulfonic acid and 2-acrylamido-2-methylpropane sulfonicacid.
 12. The process according to claim 11, wherein component B isadded to component A only during the end phase of the production processof component A after a monomer conversion of more than 80% is attained,a bond between component A and B is achieved by adding at least oneradical-forming catalyst to component A or B, in addition to component Bthere is added to A a (a) natural fiber selected from the groupconsisting of wool, silk, cotton and cellulose or a fiber selected fromthe group consisting of polyester, polyolefin, polyamide, polyvinylalcohol, polyurethane, polyurea and polyacrylonitrile, and (b) at leastone of peat, sand, clay, garden mold, ground shells of nuts or pomaceousfruit, wood flour and chitin-containing flour as neutral filling agent,the product comprising 20 to 98%-wt. of component A and 2 to 80%-wt. ofcomponent B and the content of water-extractables being less than30%-wt.
 13. In the absorption and/or retention of water and/or anaqueous solution by contact with an absorbent and the subsequentcontrolled release of water and/or the aqueous solution, the improvementwhich comprises employing as said absorbent the absorbing materialproduced according to claim 12.